Not happy
Maybe it was my mistake but I had high expectations on this lens. I had the opportunity of taking the EF 400 F4 DO IS on a couple of air shows. The Diffractive Lens technology works great on this lens but its not the same with the 70-300. It is a light wight lens and that makes it nice for traveling and not being very flashy as the big white L's. But unfortunately it is not a very sharp lens. Not hapy with it.
April 3, 2014

Almost good enough
I really wanted to love this lens - small form factor, cool diffractive optics tech, and decent IS - but in the end the image quality just wasn't there. Sharpness and contrast on the long end of the range was routinely disappointing on my 7D.
I have high hopes for the 70-300 L IS USM I just purchased to replace the DO lens.
March 27, 2013

Not as sharp as expected
This makes a good travel lens. It is versatile, relatively low weight and not too flashy. If you are looking for a sharp tele-zoom this is not the lens you need.
February 3, 2013

Small but hazy
If you really need a small and lightweight lens, this is probably the best one you'll find. The rapid focus, small size, and solid IS is nothing short of amazing. I've successfully taken some pictures handheld at night and bumping around in crowds. On the downside, the images are hazy. A large diameter unsharp-mask and black level adjustment are needed in post processing, which about doubles the noise level. Closing the aperture too much while zoomed in causes the front fresnel lens to appear in the photo.
After a few years of light use, I've accumulated quite a bit of dust inside the lens. The internal electronics also needed to be replaced out of warranty.
June 18, 2012